In the field of printing, the most common type printer has been the printer which impacts against record media that is caused to be moved past a printing line or line of printing. As is well-known, the impact printing operation depends upon the movement of impact members, such as print hammers or wires or the like, which are typically moved by means of an electromechanical derived system and which system enables precise control of the impact members.
In the field of dot matrix printers, it has been quite common to provide a print head which has included therein a plurality of print wire actuators or solenoids arranged or grouped in a manner to drive the respective print wires a very short, precise distance from a rest or non-printing position to an impact or printing position. The print wires are generally either secured to or engaged by the solenoid plunger or armature which is caused to be moved such precise distance when the solenoid coil is energized and wherein the plunger or armature normally operates against the action of a return spring.
It has also been quite common to provide an arrangement or grouping of such solenoids in a circular configuration to take advantage of reduced space available in the manner of locating the print wires in that specific area between the solenoids and the front tip of the print head adjacent the record media. In this respect, the actuating ends of the print wires are positioned in accordance with the circular arrangement and the operating or working ends of the print wires are closely spaced in vertically-aligned manner adjacent the record media. The availability of narrow or compact actuators permits a narrower or smaller print head to be used and thereby reduces the width of the printer because of the reduced clearance at the ends of the print line. The print head can also be made shorter because the narrow actuators can be placed in side-by-side manner closer to the record media for a given amount of wire curvature.
In the wire matrix printer which is utilized for receipt and journal printing operation, the print head structure may be a multiple element type and horizontally disposed with the wire elements aligned in a vertical line and supported on a print head carriage which is caused to be moved or driven in a horizontal direction for printing in line manner across the receipt or journal paper and wherein the drive elements or transducers may be positioned in a circular configuration with the respective wires leading to the front tip of the print head. In the wire matrix printer which is utilized for business forms or like record media printing operation, the print head may be oriented in a manner wherein the nose is pointed downward for printing on the form, slip or like media while the carriage and print head are moved above and across the form or media in the horizontal direction.
Alternatively, the print head may be supported and guided along a line of printing wherein the form or record media is placed on edge and the print head is caused to be driven in a vertical direction for the printing operation.
In the case of a wire matrix printer which is utilized for form or slip printing, the difference in thickness of the form or slip may require some means or mechanism for adjusting the gap or the distance between the print head and the printer platen.
Additionally, in the case of a printer which is utilized for such form or slip printing, some means or mechanism is provided to detect the presence of a slip or form as the document is being inserted into position in the printer for the printing operation. A common mechanism for detecting presence of a slip or form is an optical sensing arrangement that bridges the path of the document and detects the presence thereof.
It is in the field of slip printers and the use of optical means for detecting the presence of a slip or like document that the subject matter of the present invention is most closely associated and which provides for improved and advantageous positioning and control of such slip or document during the printing operation.
Representation documentation in the field of sensing arrangements includes U.S. Pat. No. 3,805,027, issued to L. L. Azure on Apr. 16, 1974, which discloses automatic cleaning of a fiber optics probe wherein documents are transported in a path to effect wiping the sensing end of the fiber optics probe.
U.S. Pat. No. 3,824,401, issued to T. Suzuki on July 16, 1974, discloses a photoelectric type weft sensing process and a weft sensor for carrying out weft sensing work on looms in photoelectric manner wherein interception of light, emitted on one side of the warp sheet by the weft at the moment of picking motion, is sensed on the other side while cutting off luminous noise by the warp sheet. The absence of weft at the time of picking motion will interrupt the running loom.
U.S. Pat. No. 3,844,661, issued to C. B. Birkett et al. on Oct. 29, 1974, discloses a self-cleaning optical cell for a fluid analysis system wherein the cell is provided with a wiper blade assembly to wipe opposing cell surfaces in synchronized relation with measurement of selected photosensor wavelengths.
U.S. Pat. No. 4,074,217, issued to N. Yanagawa on Feb. 14, 1978, discloses a cleaning unit for an optical system of slit exposure type in which either a receptacle or the optical system is reciprocated for scanning an original. A lens face is automatically wiped by means of a soft material for each scan.